The present disclosure relates to image forming apparatuses and image forming methods.
Typical image forming apparatuses, such as copiers, multifunction peripherals, and printers, may have a masking function for printing a document classified as having a high security level (confidentiality level). With the masking function, a confidential document is printed with some parts (such as charts and tables) of the document masked according to the level of user authorization. With respect to such a print having masked parts, a user having appropriate authorization may desire to restore the masked information.
To respond to such a desire, a certain document printer generates confidentiality-level setting information based on operations by a user. According to confidentiality-level setting information, each of a plurality of image regions of an original document is assigned a plurality of confidentiality levels for various types of document operations. The document printer then embeds the confidentiality-level setting information as a watermark image in the document and prints the document with security levels embedded therein.
A document copier compliant with the document printer retrieves the confidentiality-level setting information embedded as a watermark image from data obtained by reading the document. The document copier then acquires an authorization level of a user from user management information according to input of user information and checks the authorization level against the confidentiality-level setting information to determine regions permitted to be copied or regions permitted to be decoded.
As above, the document printer generates a document embedded with a digital watermark that indicates a plurality of regions each with a plurality of confidentiality levels set for different types of document operations. Consequently, a single document implements both copy control and decryption control according to the authorization level of a user who received distribution of the document.
However, security printing that uses digital watermarking is not protected against a risk of information leakage through photographing a print with a camera phone.
To address the risk, a certain image forming apparatus masks some parts of a document and embeds, in each masked part, information specifying the location of original image data. This ensures the security of the masked part and prevents information leakages through a print per se or photographed image of the print.